SEPTAL INNERVATION OF MOSSY CELLS IN THE HILUS OF THE RAT DENTATE GYRUS - AN ANTEROGRADE TRACING AND INTRACELLULAR LABELING STUDY

Messy cells in the hilus of the rat dentate gy rus are the main cells of origin of the dentate commissural and associational projections. Th ey project along the septotemporal axis of the dentate gyrus and may t hus in fluence the hippocampal signal flow in a longitudinal direction . To analyze the septal innervation of these hilar neurons, anterograd e tracing with Phaseolus vulgaris leucoagglutinin (PHAL) was used in c ombination with intracellular labeling of messy cells (Lucifer yellow) . Anterogradely labeled septal fibers impinge on proximal and distal d endrites of hilar messy cells but spare the cell body. In contrast, nu merous aspiny hilar neurons, presumably GABAergic interneurons, receiv e a septal innervation on their somata and proximal primary dendrites. These data demonstrate that septal fibers show a specificity for the dendritic segments of hilar messy cells. Since messy cells project pre dominantly to adjacent hippocampal lamellae, the activity of adjacent portions of the dentate gyrus may be influenced by the septal input on to these neurons.